Multi-digit fluorescent display tube with differently spaced planar control grid sections

Abstract

A multi-digit fluorescent display tube is disclosed. The display tube includes a plurality of indicating patterns arranged in a row in spaced side-by-side relational along the longitudinal width of a substrate, a filament stretched along the longitudinal direction of the indicating patterns and a control grid disposed between the filament and the indicating pattern, wherein the control grid is positioned in different plane distances with respect to the filament so as to adjust the perveance in each of the indicating patterns and to obtain an uniform brightness of the indicating patterns.

What is claimed as new and desired to be secured by letters patent of the United States is: 
     
       1. A multi-digit fluorescent display tube comprising: a substrate;   a plurality of multi-digit indicating patterns arranged in a row in spaced side-by-side relationship along the longitudinal width of said substrates,  each of said indicating patterns comprising a plurality of segmented anodes on which phosphor layers are deposited;   at least one electron emitting filament stretched along the longitudinal direction of said indicating patterns so as to be in parallel and opposite to each of said indicating patterns;   a control grid comprised of a plurality of planar sections disposed between said filament and said indicating patterns, said planar sections of said control grid being positioned at different distances with respect to said filament; whereby the perveance of each of said indicating patterns is adjusted so as to illuminate each of said indicating patterns in uniform brightness when said fluorescent display tube is energized by heating said filament with a direct current power source;   a light transparent evacuated sealed envelope in which the anodes, the filament and the control grid are disposed and through which the display may be viewed externally when the display tube is in operation.   
     
     
       2. A multi-digit fluorescent display tube as in claim 1, wherein the planar sections of the control grid form a continuous element which is at an acute angle with the plane of the substrate. 
     
     
       3. A multi-digit fluorescent display tube as in claim 1, wherein the planar sections of the control grid form a star-like configuration of alternating horizontal steps and vertical risers. 
     
     
       4. A multi-digit fluorescent display tube as in claim 3, wherein each step of said control grid is disposed opposite one of said indicating patterns. 
     
     
       5. A multi-digit fluorescent display tube as in claim 3, wherein each step of said control grid is disposed opposite several indicating patterns. 
     
     
       6. A multi-digit fluorescent display tube as in claim 1, wherein each of the planar sections of the control grid is separately connected to a power source. 
     
     
       7. A multi-digit fluorescent display tube as in claim 6, wherein each of the planar sections of the control grid is disposed opposite several indicating patterns. 
     
     
       8. A multi-digit fluorescent display tube as in claim 1, wherein the planar sections of the control grid are positioned with respect to said filament at distances hx which are obtained by the following formula:   hx = C Lx .sup.-1/2 [(Eb - (Ef · lx)].sup.5/4     wherein C is a constant determined by the fluorescent efficiency of the phosphor, the anode area, and the geometrical dimensions of the electrodes; Lx is the brightness of any one of the selected indicating patterns; Eb is the anode voltage of any one of the selected indicating patterns; l is the length between both ends of the filament; Ef is the filament voltage; and lx is the length of the filament between the right end of the filament and a point confronting any one of the selected indicating patterns when the leftmost planar section of the control grid is disposed closest to the filament and the rightmost planar section of the control grid is disposed farthest from the filament.   
     
     
       9. A multi-digit fluorescent display tube as in claim 8, wherein the planar sections of the control grid are disposed with respect to said filament at distances within a range of ± 10% of the values hx.